Non-aqueous lithium electrochemical cells typically include an anode, a lithium electrolyte prepared from a lithium salt dissolved in one or more organic solvents and a cathode of an electrochemically active material, typically a chalcogenide of a transition metal. During discharge, lithium ions from the anode pass through the liquid electrolyte to the electrochemically active material of the cathode where the ions are taken up with the simultaneous release of electrical energy. During charging, the flow of ions is reversed so that lithium ions pass from the electrochemically active cathode material through the electrolyte and are plated back onto the lithium anode. Non-aqueous lithium electrochemical cells are discussed in U.S. Pat. Nos. 4,472,487, 4,668,595, 5,028,500, 5,441,830, 5,460,904, and 5,540,741.
Recently, the lithium metal anode has been replaced with a carbon anode such as coke or graphite intercalated with lithium ions to form Li.sub.x C.sub.6. In operation of the cell, lithium passes from the carbon through the electrolyte to the cathode where it is taken up just as in a cell with a metallic lithium anode. During recharge, the lithium is transferred back to the anode where it reintercalates into the carbon. Because no metallic lithium is present in the cell, melting of the anode does not occur even under abuse conditions. Also, because lithium is reincorporated into the anode by intercalation rather than by plating, dendritic and spongy lithium growth does not occur.
Various factors influence the performance of electrochemical cells. For instance, the morphology of the polymeric matrix and of the polymeric binders in the anode and/or cathode can affect conductivity of the salts. Improved conductivity has been demonstrated by employing porous polymeric matrices and polymeric binders. One method of producing such porous structures comprises forming polymeric structures in the presence of a plasticizer such as dibutyl phthalate; upon removal of the plasticizer, pores are created in the polymer. Plasticizers can comprise up to about 50 percent of the weight of an electrochemical cell precursor prior to their removal. Current methods of removing these solvents include extraction wherein the separating agent is another organic liquid solvent such as dimethyl ether, methanol, and cyclohexane. Typically, in assembling an electrochemical cell, an electrolyte solution comprising an electrolyte solvent and salt is added to activate the electrochemical cell precursor shortly after removing the plasticizer.
Although electrochemical cells fabricated using conventional plasticizers generally demonstrate good electrochemical performance, current plasticizers must be extracted with hazardous organic solvents. The art is in search of more economical, safer, and efficient methods of preparing electrochemicals particularly methods which employ plasticizers that can be removed without the use of such solvents.